1. Field of the Invention
The invention relates to a pelletizing die for a pelletizer, comprising a base body with a front; holes which are formed in the base body for melt to pass through and which are disposed in rows; wearing-protection inserts which have holes in alignment with the holes in the base body and discharging on the front, and which are disposed in adapted recesses in the base body and are fixed by solder, and which are in alignment with the front of the base body.
2. Background Art
In the case of pelletizing dies of the generic type, knives brush over the area of the holes, cutting into pellets the strands of plastic melt that discharge there-through. These cutting surfaces are exposed to considerable wear. Therefore, they are faced for instance with wearing protection inserts of tungsten or titanium carbide containing powder metal.
U.S. Pat. No. 3,271,822 teaches a pelletizing die of the generic type, in which the ring section of the pelletizing die where the holes discharge and which the knives wipe across is provided with adjoining wearing-protection inserts of the type of square wafers. With this design, the pelletizing die cutting surface formed by the ring section may be faced entirely with wearing-protection material. A drawback resides in that provision can only be made for a bottomside soldered joint towards the base body of the pelletizing die so that there is the risk of the wearing-protection inserts peeling off. Another difficulty resides in the assembly of the wearing-protection inserts because their holes and the holes in the base body must be made flush, which requires complicated centering jobs. By alternative, the inserts would have to be drilled or eroded once they have been applied by soldering.
Furthermore, pelletizing dies of the generic type are known, in which the wearing-protection inserts are cylindrical and inserted by soldering into corresponding cylindrical blind holes in alignment with the holes formed in the base body. In this case, centering takes place quasi automatically. The fact that the inserts are soldered on the base body all over their surface area precludes them from being peeled off by the rotary knives. The drawback resides in that only approximately 50 per cent of the cutting surface which the knives wipe across can be protected by wearing-protection inserts.
U.S. Pat. No. 3,461,495 A teaches to face greater segments of the cutting surface in the form of arcuate segments of a pelletizing die with wearing-protection plates. The advantage resides in that the cutting surface is entirely faced with wear-resistant material and that again peeling off is precluded. The disadvantage resides in that the holes must be drilled or eroded subsequently in the wearing-protection plate, which is only possible if titanium carbide containing powder metal is used. This only possesses a hardness of approximately 60 HRC as opposed to tungsten carbide containing powder metal of a hardness of 70 to 90 HRC, which means a reduction of lifetime.
It is an object of the invention to embody a pelletizing die of the generic type such that as high as possible a percentage of the cutting surfaces in the form of annular segments is faced with wearing-protection inserts and that this is accompanied with ease of assembly and sufficient protection against peeling off.
According to the invention, this object is attained by the features wherein the inserts which adjoin each other in a row, where facing an adjacent insert, each have a chordal surface which is disposed at a very close distance from the chordal surface of the adjacent insert; and wherein the inserts, laterally of the chordal surface, are provided with at least one surface of an arcuate segment of a cylinder. The measures according to the invention help obtain a closed wearing protection of the appearance of a caterpillar which reaches over a row of holes and is wider than the distance of the holes in the row. Their surfaces in the shape of an arcuate segment of a cylinder are joined to the base body by soldering all over the surface area, which helps obtain a very high solidity. Ease of assembly is ensured because the surfaces of an segment of a cylinder enable the holes which have been produced in the inserts prior to their being inserted in the recesses and the holes in the base body to be centered automatically.
Further features, advantages and details of the invention will become apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing.